1. Field of the Invention
The present invention relates to an expandable MRI receiving coil. More specifically, the present invention relates to an expandable internal MRI receiving coil that has a first wire loop and a second wire loop, such that the plane of the first wire loop is positioned 90xc2x0 from the plane of the second wire loop to produce a signal that is 90xc2x0 out of phase with respect to the signal produced by the second wire loop.
2. Discussion of the Related Art
Currently there are over 1.2 million angiography procedures performed annually in the United States. These procedures are performed to provide images of the cardiac system to physicians. But traditional X-ray angiography will only provide a physician with information regarding blood flow, and the amount of an occlusion in the vessel. Moreover, the reasons for an occlusion may not be apparent because no information regarding the underlying biochemistry of the occlusion is provided by these conventional techniques.
Magnetic resonance imaging is based on the chemistry of the observed tissue. Therefore, MRI provides not only more detailed information of the structures being imaged, but also provides information on the chemistry of the imaged structures. For example, most heart attacks occur in vessels that are less than 50% occluded with plaque. But there are different types of plaque. One type of plaque is very stable and is not likely to cause problems. However, another type of plaque is unstable, if it becomes pitted or rough it is possible for blood to clot and occlude the vessel. These different types of plaque that are contained within the blood vessels can be identified by MRI as has been described, for example, by J. F. Toussaint et al., Circulation, Vol. 94, pp. 932-938 (1996). Conventionally, MR imaging of the heart has been achieved with the use of a body coil (i.e., a receiving coil that completely surrounds the torso) and specialized surface coils designed for cardiac use. However, an external body coil provides a relatively low signal to noise (SNR) when the object to be imaged is small and distant from the coil as is the heart (especially the rear portion thereof) and the aorta. Surface coils do increase the SNR in those regions close to the coil, but not to those at any distance from the coil.
Thus, in producing an MR image, it is desirable to increase the SNR as much as possible. As a general rule, the closer the receiving coil is to the object to be imaged, the better the SNR will be. Thus, to produce an image of the heart and/or the aorta, it is preferable to place a receiving coil within the body (i.e., an internal receiving coil). Additionally, for internal receiving coils, the larger the diameter of the receiving coil, the larger its area will be thereby improving its SNR.
It is an object of the present invention to obtain an MR image of an object deep within the body having a relatively high SNR. This is accomplished by using a receiving coil that can be passed through the esophagus into a position adjacent to the heart and its surrounding vessels so that an MR image of the heart, the aortic arch and the other major vessels of the heart can be made. The receiving coil has a pair of loops that are oriented 90xc2x0 relative to each other so that their respective signals are 90xc2x0 out of phase and the resultant combined image from these signals will be more symmetrical.